A crystallized glass is a material containing various crystals precipitated in a glass and exhibiting unique properties which the glass does not have. For example, precipitation of crystals of .beta.-quartz solid solution or .beta.-spodumene solid solution provides a crystallized glass having an extremely low thermal expansion or a negative thermal expansion. Moreover, the crystallized glass generally has a high mechanical strength as compared with the glass because of presence of those crystals.
In recent years, it has been attempted to precisely form the crystallized glass having such excellent properties into the shape of a thin rod, a narrow tube, a thin plate, or the like for application in the field of products, such as electronics parts and precision machine parts, which require precise dimensional accuracy.
As a method of precisely forming the glass, a forming process called redrawing is known. This process comprises the steps of preparing a glass preform with an adequate precision and heating the glass preform to a temperature higher than a softening point of the glass to perform draw forming. This process is widely used in successively producing those glass products which are required to have high precision.
In case of a conventional crystallized glass, however, it is difficult to perform the redraw forming in the manner similar to that for the glass due to the following reasons. Specifically, the conventional crystallized glass has various problems such as difficulty in softening and deformation, difficulty in drawing because of undesirable increase of devitrification during heating, and wide change in physical and chemical properties caused by variation of the amount of crystals dependent on heating. It is therefore proposed to redraw a so-called mother glass, that is, a glass before it is processed into the crystallized glass. However, the glass of this kind is designed to be easily crystallized by heating. Therefore, heating the mother glass for the redraw forming inevitably causes the undesirable devitrification to occur so that not only the dimensions but also the physical and chemical properties are difficult to be controlled.
Under the circumstances, precise forming of the crystallized glass can not presently be achieved by the redraw forming but inevitably requires machining similar to that used for ceramics, resulting in the high cost.
In view of the above-mentioned situation, it is a first object of this invention to provide a crystallizable glass which can be shaped by the redraw forming after crystallization.
It is a second object of this invention to provide a crystallized glass which can be shaped by the redraw forming.
It is a third object of this invention to provide a crystallized glass article obtained by the redraw forming.
It is a fourth object of this invention to provide a method of manufacturing a crystallized glass article by the redraw forming.